This invention relates to an apparatus which attaches to a slit lamp and provides accurate measurements of an eye. Measurements which are made include the thickness of the cornea, pupil size, the diameter of the anterior chamber, anterior chamber depth, anterior-posterior diameter and optic disc cup diameter.
Slit lamps are routinely used by ophthalmologists and optometrists to biomicroscopically examine the eye of a patient. There are no devices of which the inventor is aware for accurately measuring those parts of the eye visualized by the slit lamp. Prior art devices which make some measurements of the eye include those disclosed in the West German Offenlegungsschrift No. 2,520,445; U.S. Pat. No. 4,398,812 to Kelman; and U.S. Pat. No. 4,019,813 to Cornsweet et al.
The device described in the West German Offenlegungsschrift No. 2,520,445 consists of a microscope, keratometer and a slit lamp. The only measurement this device is capable of making is the thickness of the cornea.
The device described in the patent to Kelman measures the diameter of the anterior chamber of the eye by using two sources of light and a calibrated scale. In other words, this device is a separate unit which is not used in conjunction with a slit lamp and therefore is relatively expensive while being capable of making only a single measurement.
The device described in the patent to Cornsweet et al. is a very sophisticated instrument which uses a television camera for measuring various portions of the eye such as the thickness of the cornea, the depth of the anterior chamber, the thickness of the lens and the transparency of different portions of the eye.
In addition, ultrasonic measuring devices are presently used to measure the anterior-posterior diameter of an eye to calculate the power of magnification required for an intraocular lens implant. Such ultrasonic measuring devices are more expensive and less available than slit lamps and in addition, the effects of ultrasonic radiation on the human body are not all known. Slit lamps, on the other hand, have long been in use without harm since they use light which the eye is designed to receive.
The devices described above illustrate the types of devices currently available to an eye physician. The devices are either extremely limited in their capabilities, such as those described in the West German Offenlegungsschrift and the patent to Kelman, or the device is so very expensive that the ordinary practitioner cannot possibly afford to own such a device, like the one patented by Cornsweet et al.